1. Field
The present disclosure relates generally to an apparatus and method for improving power factor.
2. Background
The power factor of a circuit may be represented by the ratio between true power and apparent power. When considering the current waveform and voltage waveform of a circuit, the power factor may represent a measure of how much the current waveform is in phase with the voltage waveform in an alternating current (AC) power line. A power factor of 1 indicates that the current is exactly proportional (i.e., in phase) to the AC voltage. A power factor of 1 may occur when the load of a circuit is a purely resistive load, such as an incandescent lamp. Under such purely resistive loads, AC power lines may transmit their rated power. However, circuit loads generally do not allow a high power factor (i.e., a power factor close to 1). For example, the windings of an electric motor may have a significant amount of inductance and, therefore, may delay the current passing through the AC power line. Delaying the current passing through the AC power line may result in circulating current, which is current that the AC power line must carry but which is not used by the circuit load. This reduces the capacity of the AC power system, because the power supply must be rated higher than the load to provide both the load power and the circulating current.
One approach for reducing the effects of phase delayed currents involves the use of “reverse phase” dimmers. These work opposite to the way most dimmers do and turn their loads on from the start of a sinusoidal power cycle, then turn them off halfway through the sinusoidal power cycle. However, such reverse phase dimmers are designed to better drive certain types of capacitive loads and are not designed to improve power factor.
Another approach involves the use of line stabilization networks that operate in several ways. For example, capacitance may be added to the line to adjust away inductive phase delay. However, this approach provides only one fixed correction and, therefore, such addition of capacitance will be effective for only one specific inductive load. As another example, a large LC circuit may be used to provide resonance at 60 Hz. This approach effectively provides a reservoir of additional power when needed due to poor power factor. However, this approach may substantially increase the size of the system and may significantly reduce the efficiency of the system. As another example, an AC input may be converted to direct current (DC) via a high power factor converter and subsequently converted back to AC near the load, so that only the wiring between the converter and the load experiences the low power factor. However, this approach is complex and is not cost effective.
Achieving a high power factor is critical to power utilities, since customers are billed for watts delivered but are provided volt-amps. At poor power factors, the volt-amps provided may be significantly greater than the watts supplied and, therefore, the power utility must deliver (and/or circulate) power they cannot bill the customer for.